Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 231640
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
940 AM PDT TUE SEP 23 2014

.DISCUSSION...THERE IS INCREASING POTENTIAL FOR A HIGH-IMPACT
EARLY FALL RAIN EVENT ACROSS PORTIONS OF THE FORECAST AREA
WEDNESDAY INTO THURSDAY. AN ATMOSPHERIC RIVER...OR SIMPLY A LONG
STRETCH OF DEEP AND CONCENTRATED MOISTURE...IS AIMED AT THE OREGON
AND NORTHERN CALIFORNIA COAST AND IS DUE TO ARRIVE WEDNESDAY
MORNING AND WILL LAST THROUGH WEDNESDAY NIGHT.

THIS WILL BE THE FIRST WIDESPREAD RAIN ACROSS THE FORECAST AREA
SINCE THE SPRINGTIME. THIS RAIN EVENT...AT LEAST FOR AREAS ALONG
AND WEST OF THE CASCADES...WILL REPRESENT A TOP 10 PERCENT EVENT
FOR THIS TIME OF YEAR IN TERMS OF EXPECTED TOTAL RAINFALL. WILDFIRE
BURN SCARS WILL BE SUSCEPTIBLE TO FLASH FLOODING...ROCK
SLIDES...AND DEBRIS FLOWS...AND PARTICULARLY ROADS AROUND THE
HAPPY CAMP COMPLEX...JULY COMPLEX...AND BEAVER FIRE IN WESTERN
SISKIYOU COUNTY INCLUDING HIGHWAY 96 AND SCOTT RIVER ROAD. A FLASH
FLOOD WATCH AT FFAMFR HAS BEEN ISSUED FOR WEDNESDAY INTO WEDNESDAY
NIGHT FOR THE AREAS AROUND THESE BURN SCARS.

ADDITIONALLY...THE RAINS WILL CAUSE TRAVEL CONCERNS IN THE AREA...GIVEN
THAT IT`S THE FIRST SIGNIFICANT RAIN IN MORE THAN A MONTH FOR MANY
VALLEY AREAS AND THE EAST SIDE...AND OILS ON THE ROADS WILL BE
LIFTED AND CAUSE SLIPPERY ROADS ON WEDNESDAY.

LAST BUT NOT LEAST...WINDS WILL CAUSE FIRE WEATHER CONCERNS AHEAD OF
THE RAINS IN SHASTA VALLEY AND THE EAST SIDE...AND A RED FLAG
WARNING AT RFWMFR HAS BEEN ISSUED FOR THESE WINDS.

THE PREVIOUS DISCUSSION BELOW FURTHER HIGHLIGHTS THE EXPECTED
IMPACTS FROM THIS STORM. SK


&&

.AVIATION...IT WILL BE MVFR TO IFR ALONG THE COAST TODAY WITH SHOWERS
AS A WARM FRONT PUSHES IN. RAIN WILL INCREASE TONIGHT AND SPREAD
INLAND, PUSHING MVFR PAST THE COASTAL MOUNTAINS AND INTO THE
UMPQUA BASIN. THE COASTAL MOUNTAINS WILL BE PARTIALLY OBSCURED
TODAY, BECOMING FULLY OBSCURED OVERNIGHT. IT WILL BE BREEZY ACROSS
INLAND AREAS TODAY THROUGH TONIGHT LEADING TO THE POSSIBILITY OF
LOW LEVEL TURBULENCE AND ISOLATED LOW LEVEL WIND SHEAR.
PRECIPITATION WILL SPREAD FURTHER ACROSS THE AREA WITH REDUCED
CIG/VIS ON WEDNESDAY.


&&

.MARINE...UPDATED 700 AM PDT TUE 23 SEP 2014...SOUTH WINDS WILL
CONTINUE TO INCREASE LATE THIS MORNING THROUGH THE EARLY EVENING
AHEAD OF A COLD FRONT...WHICH WILL BRING PERIODS OF RAIN...STRONG
WINDS...AND HEAVY SEAS TO THE COASTAL WATERS. GALES AND VERY STEEP
AND HAZARDOUS SEAS ARE EXPECTED OVER MUCH OF THE COASTAL WATERS
LATE THIS AFTERNOON THROUGH EARLY WEDNESDAY MORNING. WINDS WILL
DIMINISH AND STEEP TO VERY STEEP WIND DRIVEN SEAS WILL SUBSIDE
LATE TONIGHT...BUT HEAVY WEST SWELL WILL BUILD ON WEDNESDAY
KEEPING SEAS STEEP INTO THURSDAY NIGHT. UNSETTLED WEATHER IS
LIKELY THROUGH THE END OF THE WEEK.


&&

.PREV DISCUSSION... /ISSUED 257 AM PDT TUE SEP 23 2014/

DISCUSSION...OUR FIRST REAL WET SEASON TYPE STORM IS JUST IN TIME
FOR THE VERY BEGINNING OF FALL. A 975 MB LOW IS NEAR 45N/140W AND
DEEPENING AS IT QUICKLY BECOMES WRAPPED UP AND OCCLUDED. ABUNDANT
COLD AIR CUMULI SHOW UP WELL ON SATELLITE ON THE BACKSIDE OF THE
DEEPENING LOW WITH A PLUME OF DEEP MOISTURE SOUTH AND EAST OF THE
LOW CENTER. THE 250MB JET DIGGING BEHIND THE LOW IS APPROACHING
190 MPH. THIS JET HELPS TO CARVE A FULL-LATITUDE UPPER TROUGH THAT
IS SLOW TO MOVE...CONSEQUENTLY THE WET COLD FRONT ASSOCIATED WITH
THIS LOW WILL BE SLOW TO MOVE AS IT PUSHES INLAND AND THE FRONT
WILL WRING OUT MUCH OF ITS MOISTURE FROM THE CASCADES WESTWARD.

PRIMARY FORECAST CONCERNS ARE POSSIBLE FLASH FLOODING NEAR
WILDFIRE BURN SCARS AND GUSTY WINDS AHEAD OF THE RAIN WITH
EXISTING FIRES.

WIND:
THIS LOW WILL REACH MATURITY QUICKLY WITH A FULLY STACKED UPPER
SYSTEM BY THIS AFTERNOON. THE WINDS CIRCULATING AROUND THE LOW
ARE QUITE STRONG ESPECIALLY ABOVE 700 MB (10,000 FEET). HOWEVER,
THE SURFACE PRESSURE GRADIENT WEAKENS CONSIDERABLY INLAND AND
WINDS BELOW 5000 FEET SHOULD BE SIGNIFICANTLY WEAKER ALTHOUGH
MIXING WILL OCCUR THIS AFTERNOON ESPECIALLY ACROSS THE HIGHER
TERRAIN EAST OF THE CASCADES. BECAUSE OF THE WEAK SURFACE PRESSURE
GRADIENT HAVE OPTED NOT TO ISSUE A WIND ADVISORY FOR THE SHASTA
VALLEY AND EAST SIDE BUT WINDS WILL STILL INCREASE TO 15 TO 25
MPH AND THE FUNNELING EFFECT NEAR WEED COULD RESULT IN LOCALIZED
WIND GUSTS TO 40 MPH.

RAIN:
THE RAIN WILL BE BENEFICIAL FOR BOTH THE ONGOING DROUGHT AND ONGOING
WILDFIRES. HOWEVER, WILDFIRES THAT HAVE BURNED THE SOIL SEVERELY
ENOUGH TO CAUSE HYDROPHOBIC SOIL WILL PRODUCE ADDITIONAL RUNOFF
FROM THE INCOMING STORM. THEREFORE A FLASH FLOOD WATCH HAS BEEN
ISSUED WITH THE FOCUS ON THE WILDFIRES IN SISKIYOU COUNTY.THIS
FLASH FLOOD WATCH COULD BE EXPANDED TO OTHER WILDFIRE AREAS IN
SOUTHWEST OREGON IF THESE HYDROPHOBIC SOIL CONDITIONS ARE PRESENT
ALONG WITH SIGNIFICANT RAINFALL RATES. THE HEAVIER RAINFALL IN
SISKIYOU COUNTY WILL OCCUR IN THE WEST AND SOUTHERN AREAS OF THE
COUNTY. MUCH OF THE RAIN WILL OCCUR TONIGHT THROUGH THURSDAY
MORNING AND WILL BE IMPRESSIVE FOR LATE SEPTEMBER, SIMILAR TO WHAT
OCCURRED LAST YEAR AROUND THIS TIME. THE AMOUNT OF MOISTURE IN THE
ATMOSPHERE IS EXPECTED TO BE EXTREMELY HIGH AND VERY UNUSUAL FOR
THIS TIME OF YEAR (LAST YEAR`S SEPTEMBER STORM WAS VERY UNUSUAL TOO)
WITH AREAS FROM THE CASCADES WEST RECEIVING NEAR OR MORE RAIN FROM
THIS STORM THAN FALLS FOR THE ENTIRE MONTH IN A NORMAL SEPTEMBER.

TEMPERATURES:
THE UPPER LOW WILL REMAIN IN THE REGION INTO THE WEEKEND DUE TO
ITS SIZE AND THE INABILITY OF ANY UPSTREAM WEATHER SYSTEM TO MOVE
IT QUICKLY. THEREFORE THE SIGNIFICANT COOLING THAT WILL OCCUR
BEGINNING WEDNESDAY WEST OF THE CASCADES WILL STICK AROUND AT
LEAST THROUGH THE WEEKEND. THERE IS LESS CONFIDENCE IN THE
FORECAST CONDITIONS EARLY NEXT WEEK AS THE MODELS BEGIN TO
DEPART. IT LOOKS LIKE SOME WARMING COULD OCCUR WITH A GENERALLY
DRY PATTERN.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 11 PM PDT WEDNESDAY FOR ORZ624-625.

CA...RED FLAG WARNING UNTIL 11 PM PDT WEDNESDAY FOR CAZ285.
     RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR CAZ281-284.
     FLASH FLOOD WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
     NIGHT FOR CAZ080-081-083.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 AM PDT WEDNESDAY FOR
     PZZ350-356.
     HAZARDOUS SEAS WARNING FROM 5 PM THIS AFTERNOON TO 5 AM PDT
     WEDNESDAY FOR PZZ350-356-370-376.
     GALE WARNING FROM 5 PM THIS AFTERNOON TO 2 AM PDT WEDNESDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THURSDAY
     FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THURSDAY FOR
     PZZ370-376.

$$

RES/RES/BTL








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